JP2023163653A - Antireflection film and method for manufacturing the same, and image display device - Google Patents

Abstract

To provide an antireflection film that, even when it is heated to high temperature in a folded state (bent state), prevents the generation of cracks in an antireflection layer and is excellent in flexibility.SOLUTION: An antireflection film (101) comprises: a hard coat film (1) that includes a hard coat layer (11) on one principal surface of a transparent film substrate (10); and an antireflection layer (5) that is provided on the hard coat layer. The antireflection layer includes at least one high refractive index layer and at least one low refractive index layer. The high refractive index layers (51, 53) are a thin film having niobium oxide as a main component. The high refractive index layer (53) arranged most separated from the hard coat layer has a film thickness of 40 nm or less and a film density of less than 4.47 g/cm3.SELECTED DRAWING: Figure 1

Description

The present invention relates to an antireflection film that includes an antireflection layer on a hard coat layer of a hard coat film, and a method for manufacturing the same. Furthermore, the present invention relates to an image display device including the antireflection film.

An antireflection film is used on the viewing side surface of an image display device such as a liquid crystal display or an organic EL display for the purpose of preventing deterioration of image quality due to reflection of external light and improving contrast. An antireflection film includes an antireflection layer made of a laminate of a plurality of thin films having different refractive indexes on a transparent film.

For example, in Patent Document 1, an SiO primer layer is provided on a hard coat film, and a niobium oxide (Nb ₂ O ₅ ) layer as a high refractive index layer and a silicon oxide (SiO ₂ ) layer as a low refractive index layer are provided on the hard coat film. An antireflection film is disclosed having an antireflection layer consisting of an alternating laminate of layers.

JP2009-47876A

In recent years, a foldable image display device (foldable display) including an organic EL panel using a foldable substrate (flexible substrate) such as a resin film has been put into practical use. As a cover window of a foldable display, an antireflection film is used, which is an antireflection layer provided on a flexible film substrate.

Foldable displays are generally stored in a folded state. In the folded state, compressive stress is applied to the inside of the folded portion (bending portion), and tensile stress is applied to the outside. When the display is folded with the display surface facing inside, the antireflection film is in a folded state with the antireflection layer forming surface facing inside. If the antireflection layer is heated to a high temperature in this state, fine cracks may occur in the antireflection layer, causing a decrease in the visibility of the display.

In view of the above, an object of the present invention is to provide an antireflection film that is difficult to crack in the antireflection layer and has excellent bending resistance even when heated to a high temperature in a folded state (bent state).

The antireflection film includes a hard coat film having a hard coat layer on one main surface of a transparent film base material, and an antireflection layer provided on the hard coat layer. In addition to the binder resin, the hard coat layer may contain fine particles having an average primary particle diameter of 10 to 100 nm. A primer layer made of an inorganic oxide may be provided between the hard coat layer and the antireflection layer. An antifouling layer may be provided on the antireflection layer.

The antireflection layer includes at least one high refractive index layer and at least one low refractive index layer. The antireflection layer may include two or more high refractive index layers, and may include two or more low refractive index layers. The antireflection layer is preferably an alternating laminate of a plurality of high refractive index layers and a plurality of low refractive index layers.

The high refractive index layer of the antireflection layer is a thin film containing niobium oxide as a main component, and the high refractive index layer disposed farthest from the hard coat layer has a film thickness of 40 nm or less and a film density of 40 nm or less. It is less than 4.47 g/ ^cm3 . When the antireflection layer includes a plurality of high refractive index layers (niobium oxide thin films), it is preferable that each high refractive index layer has a thickness of 40 nm or less and a film density of less than 4.47 g/cm ³ .

The arithmetic mean surface height of the antireflection layer is preferably 2.5 nm or more. When an antifouling layer is provided on the antireflection layer, it is preferable that the arithmetic mean surface height of the antifouling layer is 2.5 nm or more.

The antireflection film of the present invention does not easily cause cracks in the antireflection layer even when heated in a bent state with the antireflection layer forming surface on the inside, and can be suitably used for foldable displays.

FIG. 2 is a cross-sectional view showing a laminated form of an antireflection film. FIG. 2 is a cross-sectional view showing the structure of a sample used in a bending resistance test.

FIG. 1 is a cross-sectional view showing an example of a laminated structure of an antireflection film according to an embodiment of the present invention. The antireflection film 101 includes an antireflection layer 5 on the hard coat layer 11 of the hard coat film 1 . The hard coat film 1 includes a hard coat layer 11 on one main surface of a transparent film base material 10. The antireflection layer 5 is a laminate of two or more thin films having different refractive indexes, and includes at least one high refractive index layer and at least one low refractive index layer. A primer layer 3 may be provided between the hard coat layer 11 and the antireflection layer 5. An antifouling layer 7 may be provided on the antireflection layer 5.

[Hard coat film]
The hard coat film 1 includes a hard coat layer 11 on one main surface of a transparent film base material 10. By providing the hard coat layer 11 on the side on which the antireflection layer 5 is formed, mechanical properties such as surface hardness and scratch resistance of the antireflection film can be improved.

<Transparent film base material>
The visible light transmittance of the transparent film base material 10 is preferably 80% or more, more preferably 90% or more. As the resin material constituting the transparent film base material 10, for example, a resin material having excellent transparency, mechanical strength, and thermal stability is preferable. Specific examples of resin materials include cellulose resins such as triacetylcellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) Examples include acrylic resins, cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

The thickness of the transparent film base material is not particularly limited, but from the viewpoint of workability such as strength and handleability, thin layer property, etc., it is preferably about 5 to 300 μm, more preferably 10 to 250 μm, and even more preferably 20 to 200 μm.

<Hard coat layer>
Hard coat film 1 is formed by providing hard coat layer 11 on the main surface of transparent film base material 10 . The hard coat layer is a cured resin layer, and is formed by applying a composition containing a curable resin onto a transparent film base material and curing the resin component. The hard coat layer may contain fine particles in addition to the cured resin.

(curable resin)
As the curable resin (binder resin) for the hard coat layer 11, curable resins such as thermosetting resins, photocurable resins, and electron beam curable resins are preferably used. Examples of the curable resin include polyester, acrylic, urethane, acrylic urethane, amide, silicone, silicate, epoxy, melamine, oxetane, and acrylic urethane. Among these, acrylic resins, acrylic urethane resins, and epoxy resins are preferred because they have high hardness and can be photocured, and acrylic urethane resins are particularly preferred.

The photocurable resin composition contains a polyfunctional compound having two or more photopolymerizable (preferably ultraviolet polymerizable) functional groups. The polyfunctional compound may be a monomer or an oligomer. As the photopolymerizable polyfunctional compound, a compound containing two or more (meth)acryloyl groups in one molecule is preferably used.

Specific examples of polyfunctional compounds having two or more (meth)acryloyl groups in one molecule include tricyclodecane dimethanol diacrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, and trimethylol. Propane triacrylate, pentaerythritol tetra(meth)acrylate, dimethylolpropantotetraacrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol(meth)acrylate, 1,9-nonanediol diacrylate, 1, 10-Decanediol (meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, dipropylene glycol diacrylate, isocyanuric acid tri(meth)acrylate, ethoxylated glycerin triacrylate, ethoxylated pentaerythritol tetra Examples include acrylates and oligomers or prepolymers thereof. In addition, in this specification, "(meth)acrylic" means acrylic and/or methacryl.

A polyfunctional compound having two or more (meth)acryloyl groups in one molecule may have a hydroxyl group. By using a polyfunctional compound containing a hydroxyl group, the adhesion between the transparent film base material and the hard coat layer tends to improve. Examples of compounds having a hydroxyl group and two or more (meth)acryloyl groups in one molecule include pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, and the like.

The acrylic urethane resin contains a urethane (meth)acrylate monomer or oligomer as a polyfunctional compound. The number of (meth)acryloyl groups that the urethane (meth)acrylate has is preferably 3 or more, more preferably 4 to 15, and even more preferably 6 to 12. The molecular weight of the urethane (meth)acrylate oligomer is, for example, 3000 or less, preferably 500 to 2500, more preferably 800 to 2000. Urethane (meth)acrylate is obtained, for example, by reacting hydroxy (meth)acrylate obtained from (meth)acrylic acid or (meth)acrylic acid ester and polyol with diisocyanate.

The content of the polyfunctional compound in the composition for forming a hard coat layer is preferably 50 parts by weight or more based on a total of 100 parts by weight of the resin components (monomers, oligomers, and prepolymers that form a binder resin by curing). More preferably 60 parts by weight or more, and even more preferably 70 parts by weight or more. When the content of the polyfunctional monomer is within the above range, the hardness of the hard coat layer tends to be increased.

(fine particles)
When the hard coat layer 11 contains fine particles, fine irregularities are formed on the surface, which tends to improve the adhesion and bending resistance of the antireflection layer.

Examples of fine particles include inorganic oxide fine particles such as silica, alumina, titania, zirconia, calcium oxide, tin oxide, indium oxide, cadmium oxide, and antimony oxide, glass fine particles, polymethyl methacrylate, polystyrene, polyurethane, and acrylic-styrene copolymers. Crosslinked or uncrosslinked organic fine particles made of transparent polymers such as , benzoguanamine, melamine, and polycarbonate can be used without particular limitation.

The average particle diameter (average primary particle diameter) of the fine particles is preferably about 10 nm to 10 μm. The average primary particle size is a weight average particle size measured by Coulter counting method. Depending on the particle size, the fine particles have a submicron or μm-order particle size of about 0.5 μm to 10 μm (hereinafter sometimes referred to as "microparticles"), and have a particle size of about 10 nm to 100 nm. They can be broadly classified into fine particles (hereinafter sometimes referred to as "nanoparticles") and fine particles having a particle size intermediate between microparticles and nanoparticles.

When the hard coat layer 11 contains nanoparticles, fine irregularities are formed on the surface, and the adhesion between the hard coat layer 11 and the primer layer 3 and antireflection layer 5 tends to improve. As the nanoparticles, inorganic fine particles are preferred, and inorganic oxide fine particles are particularly preferred. Among these, silica particles are preferred because they have a low refractive index and can reduce the difference in refractive index with the binder resin.

From the viewpoint of forming an uneven shape with excellent adhesion to the antireflection layer on the surface of the hard coat layer 11, the average primary particle diameter of the nanoparticles is preferably 20 to 80 nm, more preferably 25 to 70 nm, and 30 to 60 nm. is even more preferable.

The amount of nanoparticles in the hard coat layer 11 may be about 1 to 150 parts by weight based on 100 parts by weight of the binder resin. From the viewpoint of forming a surface shape with excellent adhesion to the antireflection layer on the surface of the hard coat layer 11, the content of nanoparticles in the hard coat layer 11 is 20 to 100 parts by weight based on 100 parts by weight of the binder resin. Parts by weight are preferred, 25 to 90 parts by weight are more preferred, and even more preferably 30 to 80 parts by weight.

(Formation of hard coat layer)
The composition for forming a hard coat layer contains the above binder resin component and, if necessary, a solvent capable of dissolving the binder resin component. As mentioned above, the composition for forming a hard coat layer may contain fine particles. When the binder resin component is a photocurable resin, it is preferable that a photopolymerization initiator is included in the composition. In addition to the above, the composition for forming a hard coat layer also contains a leveling agent, a thixotropic agent, an antistatic agent, an antiblocking agent, a dispersant, a dispersion stabilizer, an antioxidant, an ultraviolet absorber, an antifoaming agent, and a thickening agent. , a surfactant, a lubricant, and other additives.

A hard coat layer is formed by applying a composition for forming a hard coat layer onto a transparent film base material, and removing the solvent and curing the resin as necessary. The hard coat layer forming composition can be applied by any suitable method such as bar coating, roll coating, gravure coating, rod coating, slot orifice coating, curtain coating, fountain coating, comma coating, etc. method can be adopted. The heating temperature after coating may be set to an appropriate temperature depending on the composition of the composition for forming a hard coat layer, and is, for example, about 50°C to 150°C. When the binder resin component is a photocurable resin, photocuring is performed by irradiation with active energy rays such as ultraviolet rays. The cumulative amount of irradiation light is preferably about 100 to 500 mJ/cm ² .

The thickness of the hard coat layer 11 is not particularly limited, but from the viewpoint of achieving high hardness and appropriately controlling the surface shape, it is preferably about 1 to 10 μm, more preferably 2 to 9 μm, and even more preferably 3 to 8 μm.

(Surface treatment of hard coat layer)
Before forming the antireflection layer 5 on the hard coat layer 11, a surface treatment of the hard coat layer 11 may be performed. Examples of the surface treatment include surface modification treatments such as corona treatment, plasma treatment, flame treatment, ozone treatment, glow treatment, alkali treatment, acid treatment, and treatment with a coupling agent. Vacuum plasma treatment may be performed as surface treatment. The surface roughness of the hard coat layer can also be adjusted by vacuum plasma treatment. For example, if the hard coat layer 11 contains inorganic fine particles in addition to the binder resin component (cured resin material), the resin component on the surface of the hard coat layer is likely to be selectively etched by vacuum plasma treatment, and most of the inorganic particles are etched. As a result, the abundance ratio of inorganic oxide particles on the surface of the hard coat layer and its vicinity increases, and the arithmetic mean height Sa ₁ of the surface of the hard coat layer tends to increase.

As the atmospheric gas in the vacuum plasma treatment, inert gases such as helium, neon, argon, krypton, xenon, and radon are preferred, and argon is especially preferred. The effective power density in vacuum plasma processing is preferably 0.01 W min/m cm ² or more, 0.03 W min/m cm ² or more, 0.05 W min/m cm ² or more, 0.07 W・Min/m·cm ² or more or 0.1 W·min/m·cm ² or more may be used. The effective power density is the value obtained by dividing the power density (W/cm ² ) of plasma output by the conveyance speed (m/min). The larger the effective power density, the larger the arithmetic mean height _Sa1 of the hard coat layer surface, which tends to improve the adhesion and bending resistance of the antireflection layer formed on the hard coat layer. be.

On the other hand, if the effective power density is too high, the etching of the binder resin may proceed excessively, leading to coarsening of the surface irregularities of the hard coat layer and a decrease in adhesion due to shedding of fine particles. Therefore, the effective power density is preferably 0.6 W·min/m·cm ² or less, and may be 0.43 W·min/m·cm ² or less or 0.22 W·min/m·cm ² or less.

(Surface shape of hard coat layer)
As described above, since the hard coat layer 11 contains fine particles (nanoparticles), fine irregularities are formed on the surface. Furthermore, when a hard coat layer containing fine particles is subjected to surface treatment such as plasma treatment, the unevenness tends to increase and the arithmetic mean height Sa ₁ tends to increase. The arithmetic mean height Sa is calculated according to ISO 25178 from an observed image of 1 μm square using an atomic force microscope (AFM).

The arithmetic mean height Sa ₁ of the surface of the hard coat layer 11 is preferably 2.5 nm or more, more preferably 3.0 nm or more, 3.5 nm or more, 4.0 nm or more, 4.5 nm or more, 5.0 nm or more, It may be 5.3 nm or more or 5.5 nm or more. The larger the arithmetic mean height Sa ₁ of the hard coat layer 11, the better the adhesion of the antireflection layer tends to be. In addition, when the arithmetic mean height Sa ₁ of the hard coat layer serving as the base for forming the antireflection layer 5 is large, columnar growth tends to occur during sputtering film formation of the antireflection layer 5, and the bending resistance tends to improve.

On the other hand, if the surface irregularities of the hard coat layer become coarse, sufficient adhesion may not be achieved. Therefore, the arithmetic mean height Sa ₁ of the hard coat layer surface is preferably 10 nm or less, more preferably 8.0 nm or less, even more preferably 7.5 nm or less, and may be 7.0 nm or less or 6.5 nm or less. .

[Anti-reflection film]
An antireflection film is formed by forming an antireflection layer 5 on the hard coat layer 11 of the hard coat film 1 via the primer layer 3 if necessary.

<Primer layer>
It is preferable that a primer layer 3 is provided between the hard coat layer 11 and the antireflection layer 5 of the hard coat film 1. Materials for the primer layer 3 include metals such as silicon, nickel, chromium, tin, gold, silver, platinum, zinc, titanium, indium, tungsten, aluminum, zirconium, and palladium; alloys of these metals; oxidation of these metals. compounds, fluorides, sulfides or nitrides; and the like. Among these, the material for the primer layer is preferably an inorganic oxide, and particularly preferably silicon oxide or indium oxide. The inorganic oxide constituting the primer layer 3 may be a composite oxide such as indium tin oxide (ITO).

The thickness of the primer layer 3 is, for example, about 1 to 20 nm, preferably 3 to 15 nm. If the thickness of the primer layer is within the above range, both adhesion with the hard coat layer 11 and high light transmittance can be achieved.

<Anti-reflection layer>
The antireflection layer 5 is a laminate of a plurality of thin films having different refractive indexes, and includes at least one high refractive index layer and at least one low refractive index layer. Generally, the optical thickness (product of refractive index and film thickness) of the thin film of the antireflection layer is adjusted so that the reversed phases of incident light and reflected light cancel each other out. By using a multilayer stack of a plurality of thin films having different refractive indexes, it is possible to reduce the reflectance in a wide wavelength range of visible light.

In the antireflection film 101 shown in FIG. 1, the antireflection layer 5 includes four layers: a high refractive index layer 51, a low refractive index layer 52, a high refractive index layer 53, and a low refractive index layer 54 from the hard coat film 1 side. Prepare in order. The antireflection layer is not limited to a four-layer structure, and may have a two-layer structure, a three-layer structure, a five-layer structure, or a laminated structure of six or more layers. The antireflection layer 5 is preferably an alternate laminate of two or more high refractive index layers and two or more low refractive index layers. In order to reduce reflection at the air interface, the thin film 54 provided as the outermost layer of the antireflection layer 5 (the layer furthest from the hard coat film 1) is preferably a low refractive index layer.

The high refractive index layers 51 and 53 are thin films containing niobium oxide as a main component. Since niobium oxide has a high refractive index, reflected light can be efficiently reduced by stacking it with a low refractive index layer. The refractive index of the high refractive index layer is 2.0 or more, preferably 2.2 or more. The high refractive index layer may contain metal oxides other than niobium oxide, but the content of niobium oxide is 90% by weight or more, preferably 99% by weight or more.

The thickness of the niobium oxide thin film as the high refractive index layer is preferably 40 nm or less. When the antireflection layer includes a plurality of niobium oxide thin films 51 and 53, at least the niobium oxide thin film as the high refractive index layer 53 located farthest from the hard coat layer has a thickness of 40 nm or less, and all The film thickness of the high refractive index layer (niobium oxide thin film) is preferably 40 nm or less. Due to the small thickness of the niobium oxide thin film, the antireflection layer has excellent bending resistance, and even if the antireflection film is heated in a bent state, cracks are unlikely to occur in the antireflection layer. The thickness of the niobium oxide thin film is more preferably 35 nm or less, and may be 32 nm or less or 30 nm or less.

The density of the niobium oxide thin film is preferably 4.47 g/cm ³ or less, more preferably 4.40 g/cm ³ or less, and may be 4.35 g/cm ³ or less or 4.33 g/cm ³ or less. When the antireflection layer includes a plurality of niobium oxide thin films 51 and 53, at least the niobium oxide thin film as the high refractive index layer 53 disposed farthest from the hard coat layer 11 has a film density within the above range. It is particularly preferable that the film density of all the plurality of niobium oxide thin films 51 and 53 is within the above range. The film density of the niobium oxide thin film is generally 4.0 g/cm ³ or more, and may be 4.1 g/cm ³ or more or 4.2 g/cm ³ or more. The film density is a value measured by the Rutherford backscattering (RBS) method, and the density is calculated using the film thickness determined from cross-sectional observation.

As the thickness of the niobium oxide thin film increases, the film density tends to increase. As described above, when the thickness of the niobium oxide thin film is 40 nm or less, the film density of the niobium oxide thin film does not become excessively large, and the occurrence of cracks during bending tends to be suppressed. Furthermore, the larger the surface unevenness of the base of the niobium oxide thin film (the larger the Sa), the lower the film density of the niobium oxide thin film, and the more likely the generation of cracks is suppressed.

The low refractive index layers 52 and 54 have a refractive index of 1.6 or less, preferably 1.5 or less. Examples of the low refractive index material include silicon oxide, titanium nitride, magnesium fluoride, barium fluoride, calcium fluoride, hafnium fluoride, and lanthanum fluoride. Among these, silicon oxide is preferred because it has a low refractive index, high hardness, and can efficiently reduce reflectance by laminating with a niobium oxide high refractive index layer. The low refractive index layers 52 and 54 preferably have a silicon oxide content of 90% by weight or more, more preferably 99% by weight or more. The film density of the silicon oxide thin film is preferably 2.20 g/cm ³ or less, and may be 2.15 g/cm ³ or less or 2.10 g/cm ³ or less.

When the low refractive index layer 54, which is the outermost layer of the antireflection layer, is a silicon oxide layer, the film thickness thereof is preferably greater than 85 nm. Since the low refractive index layer 54 as the outermost layer of the antireflection layer 5 is a silicon oxide layer having a thickness greater than 85 nm, the surface hardness of the antireflection layer 5 is increased, and the scratch resistance of the antireflection layer is improved. There is a tendency for the antifouling layer 7 formed thereon to have improved wear resistance.

The thickness of the low refractive index layer 54 is preferably 87 nm or more, more preferably 90 nm or more, and may be 92 nm or more, 94 nm or more, or 95 nm or more. If the film thickness of the low refractive index layer 54 is excessively large, it may cause cracks or make it difficult to design an optical design with low reflectance and excellent antireflection properties. Therefore, the film thickness of the low refractive index layer 54 is preferably 200 nm or less, more preferably 150 nm or less, and may be 130 nm or less, 120 nm or less, 115 nm or less, 110 nm or less, or 105 nm or less.

In one embodiment, the antireflection layer 5 includes, from the hard coat film 1 side, a first layer: a niobium oxide thin film as a high refractive index layer 51, a second layer: a silicon oxide thin film as a low refractive index layer 52, and a third layer: a silicon oxide thin film as a low refractive index layer 52. Layer: A niobium oxide thin film as a high refractive index layer 53, and a fourth layer: a silicon oxide thin film as a low refractive index layer 54, which is an alternating laminate of four layers in total. In another embodiment, the antireflection layer is an alternating stack of six layers each including three niobium oxide thin films as high refractive index layers and three silicon oxide thin films as low refractive index layers.

When the antireflection layer 5 is an alternate laminate of a total of four layers consisting of two high refractive index layers 51, 53 and two low refractive index layers 52, 54, the film thickness is 10 from the hard coat film 1 side. An example of a configuration includes a niobium oxide thin film 51 with a thickness of ~20 nm, a silicon oxide thin film 52 with a thickness of 35 to 45 nm, a niobium oxide thin film 53 with a thickness of 25 to 35 nm, and a silicon oxide thin film 54 with a thickness of 90 to 105 nm in this order.

(Film formation of primer layer and antireflection layer)
The method for forming the thin films constituting the primer layer 3 and the antireflection layer 5 is not particularly limited, and may be either a wet coating method or a dry coating method. Dry coating methods such as vacuum evaporation, CVD, sputtering, and electron beam evaporation are preferred because they can form a thin film with uniform thickness. Among these, sputtering is preferred because it has excellent uniformity in film thickness and can easily form a dense film.

In the sputtering method, thin films can be continuously formed while a long hard coat film is conveyed in one direction (longitudinal direction) using a roll-to-roll method, so productivity of antireflection films can be improved. In order to improve the productivity of the antireflection film, it is preferable to form all the thin films constituting the antireflection layer 5 by sputtering.

In the sputtering method, film formation is performed while introducing an inert gas such as argon and, if necessary, a reactive gas such as oxygen into a chamber. The oxide layer can be formed by sputtering using either an oxide target or reactive sputtering using a metal target. In order to form a metal oxide film at a high rate, reactive sputtering using a metal target is preferable.

By adjusting the sputtering film forming conditions, the film density of the antireflection layer can be adjusted. For example, when the discharge voltage during sputter film formation is low, the kinetic energy of sputtered particles is low and diffusion on the substrate surface is suppressed, so columnar growth is promoted and the film density tends to be low.

Furthermore, if the pressure during film formation is high, the mean free path of the sputtered particles becomes small, the directivity of the sputtered particles decreases, and the sputtered particles become more easily diffused, which tends to reduce the film density. In order to form a niobium oxide thin film with a low film density, the pressure during sputtering film formation is preferably 0.5 Pa or more, and may be 0.55 Pa or more or 0.6 Pa or more. On the other hand, if the film-forming pressure is too high, the film-forming rate will be low and productivity will be poor, so the film-forming pressure is preferably 1.5 Pa or less, and may be 1 Pa or less or 0.9 Pa or less.

When forming a thin film by a dry process such as sputtering, a thin film (at the initial stage of film formation) is strongly influenced by the underlying layer, and as the film thickness increases, it tends to have bulk-like characteristics. In particular, when the hard coat layer 11 has surface irregularities and Sa ₁ is large, the film density tends to decrease at the initial stage of film formation due to the influence of the underlying irregularities, but as the film thickness increases, the bulk characteristics There is a tendency for the film density to increase as the film density approaches.

When an antireflection film containing a thick niobium oxide thin film as a high refractive index layer is heated in a bent state with the antireflection layer forming side facing inside, cracks may occur in the antireflection layer. Even when the low refractive index layer such as silicon oxide is thick, cracks are suppressed when the niobium oxide thin film is thin, so cracks are thought to be caused by the thick niobium oxide thin film. Conceivable.

When the antireflection film is bent with the antireflection layer forming side facing inside, strain occurs in the antireflection layer in the compression direction. When heated in this state, the film base thermally expands, so that strain in the tensile direction (force to stretch the film) is generated on the surface of the thin film on the hard coat layer side. When the thickness of the niobium oxide thin film is large, the difference in strain between the front and back sides of the thin film becomes large, and the high film density makes it difficult to alleviate the strain within the film, which may lead to cracks in the antireflection layer. This is thought to be the cause.

In particular, the niobium oxide thin film 53 on the surface side of the antireflection layer 5 is more susceptible to cracking than the niobium oxide thin film 51 located on the side closer to the hard coat layer 11 because it is distorted when bent. In an anti-reflection film in which a niobium oxide thin film as a high refractive index layer and a silicon oxide thin film as a low refractive index layer are alternately laminated, optical design to reduce reflectance is performed by adding a niobium oxide thin film on the surface side of the anti-reflection layer. A configuration with a large film thickness is adopted.

In contrast, in the present invention, since the thickness of the niobium oxide thin film 53 is 40 nm or less, even if the antireflection film is heated in a bent state, the distortion of the niobium oxide thin film is small and the occurrence of cracks is suppressed. It is thought that it will be done. In addition, the hard coat layer contains fine particles and minute irregularities are formed on the surface of the hard coat layer, so when forming a thin film on top of it, columnar growth is promoted and the film density of the niobium oxide thin film is reduced. It is thought that this also contributes to improvement in bending resistance (suppression of cracks).

The arithmetic mean height Sa of the surface of the antireflection layer 5 is preferably 2.5 nm or more, more preferably 2.8 nm or more, even more preferably 3.0 nm or more, and even if it is 3.5 nm or more or 4.0 nm or more. good. The arithmetic mean height Sa of the antireflection layer 5 is preferably 8 nm or less, more preferably 7.5 nm or less, even more preferably 7 nm or less, and may be 6 nm or less or 5.5 nm or less.

<Antifouling layer>
The antireflection film preferably includes an antifouling layer 7 on the antireflection layer 5 as the outermost surface layer (top coat layer). By providing the antifouling layer on the outermost surface, the influence of contamination from the external environment (fingerprints, finger marks, dust, etc.) can be reduced, and contaminants attached to the surface can be easily removed.

In order to maintain the antireflection properties of the antireflection layer 5, it is preferable that the antifouling layer 7 has a small refractive index difference with the low refractive index layer 54, which is the outermost layer of the antireflection layer 5. The refractive index of the antifouling layer 7 is preferably 1.6 or less, more preferably 1.55 or less.

The material for the antifouling layer 7 is preferably a fluorine-containing compound. The fluorine-containing compound provides antifouling properties and can also contribute to lowering the refractive index. Among these, fluoropolymer containing a perfluoropolyether skeleton is preferred because it has excellent water repellency and can exhibit high stain resistance. From the viewpoint of improving antifouling properties, perfluoropolyethers having a main chain structure that can be rigidly arranged in parallel are particularly preferred. The structural unit of the main chain skeleton of perfluoropolyether is preferably a perfluoroalkylene oxide which may have a branch having 1 to 4 carbon atoms, such as perfluoromethylene oxide, (-CF ₂ O-) , perfluoroethylene oxide (-CF ₂ CF ₂ O-), perfluoropropylene oxide (-CF ₂ CF ₂ CF ₂ O-), perfluoroisopropylene oxide (-CF (CF ₃ ) CF ₂ O-), etc. It will be done.

The antifouling layer 7 can be formed by a wet method such as a reverse coating method, a die coating method, or a gravure coating method, or a dry method such as a CVD method. The thickness of the antifouling layer is usually about 2 to 50 nm. The greater the thickness of the antifouling layer 7, the more the antifouling property tends to improve. In addition, the greater the thickness of the antifouling layer 7, the more the antifouling properties tend to be suppressed from decreasing due to wear. The thickness of the antifouling layer is preferably 5 nm or more, more preferably 7 nm or more, and even more preferably 8 nm or more. On the other hand, the thickness of the antifouling layer is preferably 30 nm or less, more preferably 20 nm or less, from the viewpoint of forming a surface shape that reflects the uneven shape of the surface of the hard coat layer on the surface of the antifouling layer and imparting slipperiness. .

The arithmetic mean height Sa ₂ of the surface of the antifouling layer 7 is preferably 2.5 nm or more, more preferably 2.8 nm or more, even more preferably 3.0 nm or more, 3.5 nm or more, 3.7 nm or more, 3. It may be 9 nm or more or 4.0 nm or more. The arithmetic mean height Sa ₂ of the antifouling layer 7 is preferably 8 nm or less, more preferably 7.5 nm or less, even more preferably 7 nm or less, and may be 6.5 nm or less, 6 nm or less, or 5.5 nm or less.

Since the surface shape of the antifouling layer 7 reflects the surface shape of the hard coat layer 11 and the antireflection layer 5 provided thereon, the larger the arithmetic mean height Sa ₁ of the hard coat layer 11, the more the antifouling layer The arithmetic mean height _Sa2 of 7 tends to increase. Furthermore, if the antireflection layer 5 grows in a columnar manner during film formation, the arithmetic mean height Sa ₂ of the antifouling layer 7 tends to increase because the unevenness increases.

[Usage form of anti-reflection film]
The antireflection film is used, for example, by being placed on the surface of an image display device such as a liquid crystal display or an organic EL display. For example, by disposing an antireflection film on the viewing side surface of a panel containing an image display medium such as a liquid crystal cell or an organic EL cell, reflection of external light can be reduced and visibility of the image display device can be improved.

The anti-reflection film of the present invention has excellent bending resistance, and even if it is held in a bent state with the anti-reflection layer forming side facing inside, the anti-reflection layer is unlikely to crack at the bent portions, making it suitable for foldable displays. It can also be suitably used.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following specific examples.

[Production of hard coat film]
Organosilica sol (manufactured by Nissan Chemical Co., Ltd., "GRANDIC PC-1070") was added to an ultraviolet curable acrylic resin composition (manufactured by DIC, trade name "GRANDIC PC-1070") so that the amount of silica particles was 40 parts by weight per 100 parts by weight of the resin component. MEK-ST-L", average primary particle size of silica particles: 50 nm, particle size distribution of silica particles: 30 nm to 130 nm, solid content 30% by weight) were added and mixed to prepare a composition for forming a hard coat layer. did.

The above composition was applied to one side of an 80 μm thick triacetyl cellulose film (“FujiTac” manufactured by Fujifilm) so that the thickness after drying would be 4 μm, and dried at 80° C. for 3 minutes. Thereafter, using a high-pressure mercury lamp, ultraviolet rays were irradiated with an integrated light amount of 200 mJ/cm ² to cure the coating layer and form a hard coat layer.

[Example 1]
(Surface treatment of hard coat layer)
While transporting the hard coat film under a vacuum atmosphere of 0.5 Pa, the surface of the hard coat layer was subjected to argon plasma treatment at an effective power density of 0.014 W·min/m·cm ² . The arithmetic mean height Sa ₁ of the hard coat layer after the argon plasma treatment was 4.9 nm.

(Formation of primer layer)
The hard coat film after plasma treatment was introduced into a roll-to-tall type sputtering film forming apparatus, and the pressure inside the tank was reduced to 1 × 10 ^-4 Pa, and then the pressure was reduced to 0.5 Pa while running the film. An ITO primer layer with a thickness of 2 nm was formed by sputtering under conditions of introducing argon gas and oxygen gas at a volume ratio of 98:2, power source: MFAC, and input power: 6 kW. For forming the ITO primer layer, a sintered target containing indium oxide and tin oxide at a weight ratio of 90:10 was used as a target material.

(Formation of antireflection layer)
Following the formation of the ITO primer layer, reactive sputtering was performed to form a first layer: ₅ layers of 14 nm Nb ₂ O (refractive index: 2.32), a second layer: ₂ layers of 40 nm SiO (refractive index: 1.46). ), a third layer: 29 nm Nb ₂ O ₅ layers, and a fourth layer: 94 nm 2 SiO ₂ layers were sequentially formed to form an antireflection layer. For forming the _five Nb ₂ O layers (first and third layers), an Nb target was used, and argon gas and oxygen gas were introduced at a volume ratio of 90:10 so that the pressure was 0.6 Pa. , Sputtering was performed with input power: 30 kW. To form _two SiO layers (second and fourth layers), a Si target was used, and argon gas and oxygen gas were introduced at a volume ratio of 70:30 so that the pressure was 0.5 Pa. Sputtering was performed with power: 20 kW.

(Formation of antifouling layer)
Using a dried and solidified fluorine-based antifouling coating agent (SHIN-ETSU SUBELYN KY1903-1 manufactured by Shin-Etsu Chemical Co., Ltd.) as a vapor deposition source, a film was formed on the antireflection layer by vacuum evaporation at a heating temperature of 260°C. An antifouling layer with a thickness of 7 nm was formed.

[Example 2]
The discharge power during plasma treatment was changed, and the effective power density was set to 0.14 W·min/m·cm ² . Other than that, the plasma treatment of the hard coat layer, the formation of the antireflection layer, and the formation of the antifouling layer were carried out in the same manner as in Example 1 to produce an antireflection film. The arithmetic mean height Sa ₁ of the hard coat layer after the argon plasma treatment was 5.7 nm.

[Comparative example 1]
In forming the antireflection layer, the film thickness of each layer was changed as shown in Table 1. Other than that, the plasma treatment of the hard coat layer, the formation of the antireflection layer, and the formation of the antifouling layer were carried out in the same manner as in Example 1 to produce an antireflection film.

[Comparative example 2]
In forming the antireflection layer, the pressure during film formation of the first and third Nb ₂ O ₅ layers was changed to 0.4 Pa. Other than that, the plasma treatment of the hard coat layer, the formation of the antireflection layer, and the formation of the antifouling layer were carried out in the same manner as in Example 1 to produce an antireflection film.

[evaluation]
<Surface shape>
Using an atomic force microscope (AFM), the surface shapes of the hard coat layer and the antireflection film (antifouling layer) were measured under the following conditions, and the arithmetic mean surface height Sa was measured according to ISO 25178.
Device: Bruker Dimension 3100, Controller: NanoscopeV
Measurement mode: Tapping mode Cantilever: Si single crystal Measurement field of view: 1μm x 1μm

<Thin film thickness and film density>
A sample for cross-sectional observation was prepared by processing an antireflection film using a focused ion beam processing device (Hitachi High-Tech's "FB2200"), and the cross section was observed using a field emission transmission electron microscope (JEOL's "JEM-2800"). The thickness of the thin film constituting the antireflection layer was measured.The film density of the thin film constituting the antireflection layer was measured by the Rutherford backscattering (RBS) method.In calculating the film density, it was obtained from cross-sectional observation. The film thickness was used.

<Bending resistance test>
Cut the anti-reflection film into a size of 10 mm width x 100 mm length, and bend it 180 degrees so that the surface on the anti-reflection layer side faces inside, so that the bending radius is constant at D/2 as shown in Figure 2. Both ends in the length direction were attached to a spacer having a thickness of D. This sample was heated in an oven at 100° C. for 30 minutes, then taken out, and the presence or absence of cracks in the curved portion (white turbidity of the antireflection layer) was visually confirmed. An evaluation was performed when the spacer thickness D was 9.2 mm, 7.8 mm, and 5.2 mm (bending radius D/2 was 4.6 mm, 3.9 mm, and 2.6 mm), and no cracks were found. The minimum value of the bending radius was taken as the bending resistance radius.

The effective power density of the plasma treatment of the hard coat layer of the antireflection film of Examples and Comparative Examples, the arithmetic mean height Sa ₁ after plasma treatment, the film thickness of each layer constituting the antireflection layer, the first layer and the third layer. Table 1 shows the film density of the _five Nb ₂ O layers, the arithmetic mean height Sa ₂ of the antifouling layer surface, and the bending resistance radius of the antireflection film.

In Comparative Example 1 in which the thickness of the third layer was 95 nm, the bending radius was 4.6 mm, whereas the thickness of the _five Nb ₂ O layers (first layer and third layer) was Examples 1 and 2, which had a diameter of 40 nm or less, had a smaller bending radius than Comparative Example 1 and were excellent in bending resistance. In Examples 1 and 2, the film density of the third layer was lower than that in Comparative Example 1, and it is thought that the reduction in film density contributed to the improvement in bending resistance.

In Comparative Example 2, although the thickness of the third layer was the same as in Examples 1 and 2, the bending resistance was poor. In Comparative Example 2, the pressure during the formation of the _five Nb ₂ O layers was low and the film density was high, so it is thought that the bending resistance was lower than in Examples 1 and 2.

In a comparison between Example 1 and Example 2, Example 2, in which the plasma treatment of the hard coat layer had a higher electric power, had a smaller bending radius and was superior in bending resistance. In Example 2, where the discharge power is large, columnar growth is promoted due to the large surface unevenness (arithmetic mean height Sa ₁ ) of the hard coat layer, and the film density is difficult to increase, which contributes to improving the bending resistance. It is thought that there are.

1 Hard coat film 10 Transparent film base material 11 Hard coat layer 3 Primer layer 5 Antireflection layer 51, 53 High refractive index layer (niobium oxide layer)
52, 54 Low refractive index layer (silicon oxide layer)
7 Antifouling layer 101 Antireflection film

Claims (11)

A hard coat film comprising a hard coat layer on one main surface of a transparent film base; and an antireflection film comprising an antireflection layer provided on the hard coat layer of the hard coat film,
The antireflection layer includes at least one high refractive index layer and one low refractive index layer,
The high refractive index layer is a thin film containing niobium oxide as a main component,
The high refractive index layer located farthest from the hard coat layer has a film thickness of 40 nm or less and a film density of less than 4.47 g/cm ³ .
Anti-reflective film. The antireflection film according to claim 1, wherein the antireflection layer includes two or more of the high refractive index layers. The antireflection film according to claim 2, wherein all the high refractive index layers are thin films containing niobium oxide as a main component, have a thickness of 40 nm or less, and a film density of less than 4.47 g/cm ³ . The antireflection film according to any one of claims 1 to 3, wherein the antireflection layer has an arithmetic mean surface height of 2.5 nm or more. The antireflection film according to any one of claims 1 to 3, comprising a primer layer made of an inorganic oxide between the hard coat layer and the antireflection layer. The antireflection film according to any one of claims 1 to 3, wherein the hard coat layer contains a binder resin and fine particles having an average primary particle size of 10 to 100 nm. The antireflection film according to any one of claims 1 to 3, comprising an antifouling layer on the antireflection layer. The antireflection film according to claim 7, wherein the antifouling layer has an arithmetic mean surface height of 2.5 nm or more. A method for producing the antireflection film according to any one of claims 1 to 3, comprising:
A method for producing an antireflection film, comprising forming the antireflection layer by a sputtering method. The method for producing an antireflection film according to claim 9, wherein the pressure when sputtering the high refractive index layer of the antireflection layer is 0.5 Pa or more. An image display device, wherein the antireflection film according to any one of claims 1 to 3 is disposed on the viewing side surface of an image display medium.

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